These ancient lands: a geological journey through the Cairngorms with Alan McKirdy

THE geology of the Cairngorms was created on a timeline that stretches far back into the mists of the dim and distant past. Much of the Cairngorms are underlain by granite that formed deep within the Earth’s crust and "surfaced" as the overlying layers of rock were stripped away by the forces of erosion – ice, wind and water.

The geologically recent Ice Age re-engineered the Cairngorm landscape in dramatic fashion. The Lairig Ghru, an incised glen that runs north-west to south-east, is one of the most prominent landmarks in the Cairngorms.This iconic landform was carved by a fast-moving stream of ice that cut deep into the granite massif. The bedrock is hard and, although the area has been heavily glaciated, the Cairngorms boast 20 Munros, the highest of Scotland’s peaks. In fact, four of the five highest mountains in the country are in the Cairngorm range.

The area attracts climbers, walkers and assorted adventurers who want to pit themselves against some of the most challenging conditions to be found anywhere in the UK. The plants and animals of the high plateau also need to be hardy to survive the severe winter conditions.

The higher reaches of the mountains are rich in montane vegetation such as lichen heath and other habitats that support many rare species.

Between around 30,000 and 15,000 years ago, even the very highest ground of the Cairngorms was overtopped by ice. Relatively fast-moving streams of ice cut great scars into the bedrock, such as at Glen Avon and, perhaps most spectacularly of all, at the Lairig Ghru mountain pass. In contrast, the ice that covered the high plateau was thin and slow-moving. As it was probably frozen to the rock surface, it didn’t cut deep or modify this undulating surface to any great extent. This explains why the tors, which were initiated before the great freeze, survived largely intact.

Around 15,000 years ago, at the end of the last cold snap, the climate started to warm and pioneer grasses gained a toehold. All of these events can be reconstructed and dated by the analysis of pollen grains recovered from sediments that built up at the bottom of adjacent lochs and in accumulated peat deposits.

Around 12,900 years ago, the climate cooled once again with an average summer temperature of around 5°C. Small glaciers reappeared on the higher ground in the Cairngorms but this return to glacial conditions only lasted for 1,500 years. By 11,500 years ago, the last of these short-lived glaciers had melted and we entered the geological phase we currently enjoy – the Anthropocene. It was so named because of the effect that Man started to have on the face of the planet, its ecosystem and ultimately its climate.

On each occasion when the ice melted in response to a changing climate, deluges of icy water were liberated to flow across the landscape. Rivers and streams act like conveyor belts, transporting these water torrents, boulders, cobbles, sand and mud from the higher ground to lower flatter lands and onwards to the sea. They are powerful

agents of change that have been scouring the landscape for millennia.

One of the sites that illustrates the volumes of meltwater involved lies to the north of the Cairngorms on the River Findhorn at Randolf’s Leap. The "boiling" torrents of water and their sediment load had the ability to act as a powerful rock-saw that sliced through the underlying bedrock.

The melting waters flowed more gently at other times. Huge braided streams and rivers flowed from the melting ice across the lower ground excavated by the glaciers. Great spreads of gravel and sand were deposited in a geological instant. Later erosion by rivers has cut through these deposits to reveal their extent.

Another feature of this de-glaciation or ice melting process was the creation of great ice-dammed lakes.The larger valley glaciers took longer to melt, blocking the escape route of water melting from adjacent ice fields. Small temporary areas of standing water resulted.

Evidence for this is found in Glen Quoich and Glen Derry in the south and Lairig Ghru and Gleann Einich further to the north. The dynamic process of landscape change and renewal continues to this day.

Another spectacular, and accessible, place to see the effects of the torrents of water flowing from the melting ice is at the Burn o’ Vat just to the west of Aboyne, Aberdeenshire. A deep, roughly circular gouge was cut into solid granite by rushing meltwaters from the adjacent high ground. Large boulders got trapped in a small depression and, over time, they circulated round and round creating a deeper and more pronounced pothole that is now some 15m deep and 18m in diameter at its widest point.

After the ice melted and the torrents subsided, the stream that now passes through the depression diminished to a trickle. This site forms part of the Muir of Dinnet National Nature Reserve, and has a visitor centre with toilets and ample parking.

Traces of the past: a visitor's guide

Weather can change in a heartbeat in the sub-Arctic environment of the Cairngorm plateau – from bracing at the beginning of a walk to extreme conditions a short time later. The places of interest described below are easily reached and safe to visit in all but the most extreme weather conditions. None of them are places where visitors may find themselves in unfamiliar, challenging terrain. There are many other sources of information available to inform the more adventurous visitor on all issues related to access to the countryside; see www.outdooraccess-scotland.com

Linn of Dee

The dramatic falls at the Linn of Dee are to be found a few kilometres west of Braemar. NTS have provided parking and toilet facilities.The River Dee, on its progress westwards, has carved a deep cleft through Dalradian rocks.This is also an access point to Glen Lui that runs north

westwards to Ben Macdui and the Lairig Ghru beyond. NTS run guided walks with qualified leaders for anyone who wants a real mountain experience. Booking ahead is essential for this trip.

Cairngorm funicular railway

The railway runs from a car park at the end of the access road to the Cairngorm ski resort up to the edge of the plateau summit. In winter, it is very much the skier and snowboarder’s domain, but the upper station, by the Ptarmigan restaurant, also affords panoramic views across glaciated landscapes of the western part of the Cairngorms. The viewing terrace, shop and exhibition about the flora and fauna of the mountain, provide an additional attraction for those not equipped for sport.

Cairngorms from the roadside

For those who want to appreciate the landscapes without pulling on their walking boots, the road network that runs around, and partly through, the Cairngorm massif is an excellent way to get a flavour of the place. The A939 runs between Cockbridge and Tomintoul, the highest village in the Highlands. It’s one of the most famous routes in Scotland as it’s often the first to be closed with the onset of wintry weather. Alpine in some aspects, it’s a roller-coaster ride through some of the highest land the country has to offer. It also gives an excellent flavour of the landscapes of this unique upland area. For those who haven’t the time or inclination to do serious walking, it’s the armchair way to see some of this rugged terrain up close.

The A93 from Bridge of Cally to Braemar also takes the motorist through some spectacular scenery, following the glaciated valley of Glen Shee northwards by way of the Clunie Water to Braemar. From there, the A93 runs eastwards to Aberdeen, never straying far from the banks of the River Dee.

The A9 runs along the western flank of the higher ground and provides spectacular views of some of the main landscape features, such as the Northern Corries.

Roches moutonnées

These roadside rock exposures show the power of the ice to erode solid rock. The granites have been smoothed by the passage of the ice, forming an undulating surface known as a "glacial pavement". These features of interest are located by the side of the road adjacent to the A95, near Dulnain Bridge just to the south of Grantown-on-Spey.

This is an edited extract from The Cairngorms: Landscapes In Stone by Alan McKirdy (Birlinn, £6.99), one of a series of books on Scottish geology which help amateurs and experts alike to understand the ground beneath their feet. Other titles available are Edinburgh, Skye, and Arran www.birlinn.co.uk